Primordial deuterium abundance from calculations of $p(n,\gamma)$ and $d(p,\gamma)$ reactions within potential-model approach

Abstract

The $p(n,\gamma)$ and $d(p,\gamma)$ reactions are key nuclear inputs for Big Bang nucleosynthesis. In this work, both reactions are analyzed within a consistent two-body potential framework based on the Malfliet-Tjon interaction, including contributions from both $E1$ and $M1$ transitions. A single scaling factor $\lambda$ controlling the low-energy scattering dynamics is constrained by the $p(n,\gamma)$ and propagated consistently to the $d(p,\gamma)$. The obtained abundance, $\mathrm{D/H} = 2.479^{+0.350}_{-0.177}\times 10^{-5}$, is in good agreement with values inferred from metal-poor damped Lyman-$\alpha$ systems. The modest variations of $\lambda$ lead to a significant change in the predicted $\mathrm{D/H}$ ratio and light-element abundances.